Blood and blood plasma viscosity may become abnormal due to a variety of pathologic conditions. While the viscosity of full blood is primarily determined through hematocrit, changes in viscosity are observed in conjunction with various diseases, primarily those associated with altered protein levels. For example, infection, infarction, hypertension, or diabetes may alter plasma viscosity, which in turn may complicate the condition. Protein-induced hyperviscosity may lead to an elevated risk of atherosclerosis. Additionally, one of the adverse effects of smoking is elevated plasma viscosity, which may be the link between cigarette consumption and cardiovascular disease.
Non-pathogenic conditions may also influence blood rheology, including bed rest (e.g., associated with prosthetic implants), pregnancy and aging. Viscosity changes during the aging process may also be attributed to indirect effects, such as age-related changes in habits (e.g., increased smoking or lack of exercise).
Accordingly, using plasma viscosity as a diagnostic tool to allow early detection of diseases is advantageous. Even where there is no direct causal relationship between disease and plasma viscosity, measurement of plasma viscosity nonetheless becomes a crucial element in sever hemorrhage when hemodilution leads to dramatically lowered hematocrit and plasma viscosity plays an important role. Blood expansion with high-viscosity fluids enhances capillary perfusion and thus tissue oxygenation.
Accordingly, for many related purposes, including viscosity-related research, diagnosis of cardiovascular disease, or monitoring of the blood resuscitation process, a viscometer that is capable of fast serial measurement with low volumes is desirable. Mechanical devices for the measurement of fluid viscosity are presently available, but they continue to pose disadvantages such as slow measurements, lack of robustness, the need for meticulous cleaning and susceptibility to operator errors. The most widely used conventional mechanical devices are: the falling-ball viscometers (wherein the time required to produce a result usually measures from between 1 minute and 20 minutes), which have high susceptibility toward uncleanliness and the occurrence of solid particles or air in the fluid; flow-resistance viscometers, such as capillary or Oswald-type viscometers, which need high volumes of fluid and require measurement times in the order of minutes; and cone-and-plate viscometers, which have the same disadvantages of the flow-resistance viscometers.
Additionally, a class of molecules known as molecular rotors have been used to probe fluid viscosity in vitro. Molecular rotors are fluorescent molecules with a quantum yield that is dependent on the free volume—and thus the viscosity—of their environment. Molecular rotors form a twisted internal charge transfer (TICT) complex upon excitation. These molecules have a preferred de-excitation pathway of internal conversion through rotation about a C═C double bond. This internal rotation rate depends on the viscosity of the solvent, leading to a viscosity-dependent quantum yield. For example, 9-(2,2-dicyanovinyl)-julolidine (DCVJ) has been used to probe fluid viscosity in vitro by dissolving the DCVJ in a fluid having a viscosity to be measured, and subsequently observing the fluorescence emission. However, because the rotors are dissolved in the fluid to be observed, the applications are limited to in vitro applications.